A speaker is generally a device which transduces electric signals into sound signals. In particular, a dynamic speaker has a structure in which a voice coil, installed in a magnetic circuit, is displaced up and down in dependence on the electric signals supplied to it. The voice coil vibrates a mechanically connected diaphragm so as to reproduce sound signals. The dynamic speaker is widely used due to its simple structure, excellent reproduction characteristics and wide range of sound reproduction as well as high modulation effect. The dynamic speaker, on the other hand, also has some drawbacks: it is relatively large in size, it is very heavy in weight and its tone quality tends to be easily influenced by temperature or humidity.
Recently, continuous efforts have been made to develop a piezo-electrical film speaker, utilizing piezo-electrical elements to reciprocally transduce electrical energy and mechanical energy. Above all, a film speaker utilizing a number of piezo-electrical elements would enlarge the range of use for a piezo-electrical film speaker which has previously been used only as a speaker for high level sounds, so that it can become a substitute for dynamic speakers.
Compared with the former dynamic speaker, a film speaker possesses advantages attributable to its small size, light weight and low price. Consistently equal quality can be obtained independent of the humidity or temperature. Film speakers can also be used for ornamental purposes by being installed on a wall or desk and by being manufactured in various shapes such as a dome, arch, quadrilaterial, or cylinder.
In addition, a stereo type should be adopted for the speaker system in order to produce some vibrant stereophonic sound.
The conventional stereo system utilizing dynamic speakers, as shown in FIG. 1, comprises input terminal 1 which receives input electrical signals, a stereo separator 2 which separates the input signals, amplifiers 3, 3' which amplify each separate signal, and speakers 4, 4' which reproduce sound signals in dependence on the amplified electrical signals.
The separated signals, which have been separated into left and right stereo signals by the stereo separator 2, are amplified by respective amplifiers 3, 3' and finally are transmitted to the piezo-electrical element to operate the film diaphragm of the speaker.